A physicochemical process for refining metal surfaces is described and claimed in Michaud et al U.S. Pat. No. 4,491,500, issued Jan. 1, 1985, which process involves the development, physical removal and continuous repair of a relatively soft coating on the surface. The mechanical action required is preferably generated in a vibratory mass finishing apparatus, and very smooth and level surfaces are ultimately produced in relatively brief periods of time.
Zobbi et al U.S. Pat. No. 4,705,594, issued Nov. 10, 1987, provides a composition for use in the physicochemical mass finishing of metal surfaces of objects. The composition includes oxalic acid, sodium nitrate, and hydrogen peroxide, so formulated as to rapidly produce highly refined surfaces.
Michaud U.S. Pat. No. 4,818,333, issued Apr. 4, 1989, provides a physicochemical process for refining relatively rough metal surfaces to a condition of high smoothness and brightness, which is characterized by the use of a non-abrasive, high-density burnishing media.
Although the processes and chemical compositions of the foregoing inventions are most effective and satisfactory for their intended purposes, they are subject to certain limitations. In particular, the compositions disclosed therein are not effective, or at least not sufficiently so as a practical matter, for the refinement of magnetic stainless steel surfaces.
The prior art discloses a wide variety of compositions for treating metal surfaces for various purposes, in some instances having particular applicability to surfaces of stainless steel. For example, Gibson U.S. Pat. No. 2,577,887, issued Dec. 11, 1951, provides coatings for the protection of stainless steel during mechanical working operations. The composition comprises oxalic acid or ferric oxalate, an accelerator (preferably the ferric ion), and a member of the group of anions consisting of chloride, bromide, ferricyanide and thiocyanate; at least about two percent chloride ion, or equivalent anion, in the solution is deemed effective.
In U.S. Pat. No. 2,617,749, issued Nov. 11, 1952, Gibson provides a bath containing oxalic acid, thiocyanate, peroxide and ferric ion, also for producing protective coatings on stainless steel. It appears that thiocyanate constitutes at least about 25 weight percent of the active ingredients used, and the threshold quantity of that constituent, which is 1.5 percent of the solution, is deemed by the patentee to be "extremely critical."
Springer et al U.S. Pat. No. 2,649,361, issued Aug. 18, 1953, discloses a process for dissolving metals using an aqueous solution of one or more cyanides and one or more nitro-substituted aromatic compounds; ammonium and alkali metal cyanides, and m-nitrobenzene sulfonic acid, are specifically mentioned.
Goodspeed et al U.S. Pat. No. 2,800,421, issued July 23, 1957, provides a composition and method for coating stainless steel utilizing oxalic acid, halide and/or thiocyanate ion, and an organic nitro-compound; at least one percent of the halide ion or thiocyanate ion, based upon the total solution, is employed.
An aqueous solution for producing a black immersion coating on nickel is provided by Grunwald U.S. Pat. No. 3,097,117, issued July 9, 1963; in addition to a strong inorganic acid, the solution contains 0.05 to 1.0 mole per liter of an aromatic nitro derivative and 0.01 to 0.5 mole per liter of an inorganic thiocyanate.
In accordance with Freeman et al U.S. Pat. No. 3,459,604, issued Aug. 5, 1969, compositions useful in forming lubricant-carrying coatings on stainless steel may include, in addition to a major amount of oxalic acid, one or more accelerator compounds such as up to about 20 grams (and preferably one to ten grams) per liter of m-nitrobenzene sulfonic acid, and one to ten grams per liter of alkali metal and ammonium thiocyanates.
Ashdown U.S. Pat. No. 3,547,711, issued Dec. 15, 1970, provides a process for coating steel surfaces. In Example One, an oxalate coating is produced using a solution containing (on a per liter basis) 40 grams of oxalic acid, 1.5 grams of sodium metal dinitrobenzene sulfonate (expressed as NO.sub.2), 2.6 grams of ammonium thiocyanate (expressed as SCN) and 5.0 grams of ammonium bifluoride (expressed as F).
In U.S. Pat. Nos. 4,724,041 and 4,724,042, both issued on Feb. 19, 1988, Sherman teaches compositions and methods for preparing ferrous metal components for electroplating, the method being carried out by agitating the components in a vibratory finishing vessel while they are immersed in a solution containing oxalic acid, a phosphorous sequestering agent, an ammonifying agent (for pH adjustment), a surfactant, and a carrier agent; in accordance with No. 4,724,042, monoethanolamine, carried by an absorbent such as diatomaceous earth, may be used for pH control.
Despite such teachings of the prior art, a demand remains for compositions, aqueous solutions, and methods that are effective for use in the physicochemical refinement of magnetic stainless steel surfaces.
Accordingly, the broad objects of the present invention are to provide novel compositions and novel aqueous solutions made from them, which solutions are effective for the refinement of metallic objects, and particularly those having magnetic stainless steel surfaces, by the mass finishing thereof; and to provide novel mass finishing processes utilizing such solutions.
Related objects of the invention are to provide such compositions, solutions and processes, by which surface refinement is achieved at high rates of speed, with highly uniform metal removal under suitable conditions, and without significant pitting, etching, corrosion or other intergranular attack of the workpiece surfaces.
More specific objects are to provide such compositions, solutions and processes with and by which surface refinement is achieved without significant pitting, etching, corrosion or other intergranular attack of workpiece surfaces, including those surfaces that are present at oxygen-starved sites; to provide such compositions, solutions and processes by and from which no objectional level of odor is generated; and to provide such compositions, solutions and processes which are used and carried out with particular effectiveness in open, vibratory mass finishing equipment.